As a quantity of mobile terminals increases, users have higher requirements for a data volume, and a high frequency with rich bandwidth resources is introduced as a backhaul resource and an access frequency, to form a high-low frequency hybrid communications system, that is, both low-frequency communication and high-frequency communication can be performed between a base station and UE (user equipment). A beam of a high frequency needs to be relatively narrow, to ensure a particular transmission distance. However, a coverage area of a narrow beam system is limited. Therefore, to maximize an antenna gain, narrow-beam scanning alignment needs to be performed between a transmit end and a receive end. That is, when the transmit end scans a transmit beam, the receive end needs to scan a corresponding receive beam, so that synchronization of a high frequency frame is implemented. Only in this way, normal communication can be implemented between the base station and the UE.
In the current high-low frequency hybrid communications system, the base station has four transmit beams, and the UE has four receive beams (RX1 to RX4). If it is specified that a transmit beam and a receive beam that are aligned between the transmit end and the receive end are Z1 and RX1, respectively, the UE needs to receive, by using the receive beam RX1, all signals transmitted by using the transmit beam Z1. Only in this way, all data sent by the base station can be received.
In an actual case, the UE does not know when the base station scans a transmit beam, and therefore is uncertain about a synchronization point of a high frequency frame of the UE, that is, the UE is uncertain about a receive moment of the high frequency frame. Therefore, a case shown in FIG. 1 may occur. The UE scans a receive beam RX1 at a moment between a start moment and an end moment at which the base station scans a transmit beam Z1. In this case, the UE can never continuously receive a complete signal in the transmit beam Z1 and the receive beam RX1. It can be learned that, in the prior art, synchronization of the high-frequency frame cannot be implemented between the UE and the base station, and consequently, the UE cannot receive complete data transmitted by using a high frequency frame.